Flooding is a pervasive natural hazard—costly in both human and economic terms—and climate change will probably exacerbate risks around the world. Mountainous areas, such as the densely populated European Alps, are of particular concern as topography and atmospheric conditions can result in large and sudden floods. In addition, the Alps are experiencing a high warming rate, which is probably leading to more heavy rainfall events. Here, we compile palaeoflood records to test the still uncertain impact these climatic trends might have on flood frequency and magnitude in the European Alps. We demonstrate that a warming of 0.5–1.2 °C, whether naturally or anthropogenically forced, led to a 25–50% decrease in the frequency of large (≥10 yr return period) floods. This decreasing trend is not conclusive in records covering less than 200 years but persistent in those ranging from 200 to 9,000 years. By contrast, extreme (>100 yr) floods may increase with a similar degree of warming in certain small alpine catchments impacted by local intensification of extreme rainfall. Our results show how long, continuous palaeoflood records can be used to disentangle complex climate–flooding relationships and assist in improving risk assessment and management at a regional scale.
This is a preview of subscription content
Subscribe to Nature+
Get immediate online access to the entire Nature family of 50+ journals
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
The authors declare that the palaeoflood data supporting the findings of this study (Extended Data Table 1) are available in the NOAA database at the following address: https://www.ncei.noaa.gov/access/paleo-search/study/34712. The temperature data from Extended Data Table 4 are all available in the NOAA or PANGEA repositories.
Center for Research on the Epidemiology of Disasters (UNISDR). The human cost of natural disasters: A global perspective, 58 pp. Retrieved from http://cred.be/sites/default/files/The_Human_Cost_of_Natural_Disasters_CRED.pdf (CRED, 2015)
Dottori, F. et al. Increased human and economic losses from river flooding with anthropogenic warming. Nat. Clim. Change 8, 781–786 (2018).
Fowler, H. J. et al. Anthropogenic intensification of short-duration rainfall extremes. Nat. Rev. Earth Environ. 2, 107–122 (2021).
Auer, I. et al. HISTALP—historical instrumental climatological surface time series of the Greater Alpine Region. Int. J. Climatol. 27, 17–46 (2007).
Pepin, N. et al. Elevation-dependent warming in mountain regions of the world. Nat. Clim. Change 5, 424–430 (2015).
Giorgi, F. et al. Enhanced summer convective rainfall at Alpine high elevations in response to climate warming. Nat. Geosci. 9, 584–589 (2016).
Ménégoz, M. et al. Contrasting seasonal changes in total and intense precipitation in the European Alps from 1903 to 2010. Hydrol. Earth Sci. Syst. 24, 5355–5377 (2020).
IPCC: Summary for Policymakers. In IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (eds Pörtner, H.-O. et al.) (IPCC, 2019).
Kundzewicz, Z. W. et al. Differences in flood hazard projections in Europe—their causes and consequences for decision-making. Hydrol. Sci. J. 62, 1–14 (2016).
Blöschl, G. et al. Changing climate both increases and decreases European river floods. Nature 573, 108–111 (2019).
Mangini, W. et al. Detection of trends in magnitude and frequency of flood peaks across Europe. Hydrol. Sci. J. 63, 493–512 (2018).
Hundecha, Y., Parajka, J. & Viglione, A. Assessment of past flood changes across Europe based on flood-generating processes. Hydrol. Sci. J. 65, 1830–1847 (2020).
Blöschl, G. et al. Increasing river floods: fiction or reality? WIREs Water 2, 329–344 (2015).
Bertola, M., Viglione, A., Lun, D., Hall, J. & Blöschl, G. Flood trends in Europe: are changes in small and big floods different? Hydrol. Earth Syst. Sci. 24, 1805–1822 (2020).
Tarasova, L. et al. Causative classification of flood events. WIREs Water 6, e1353 (2019).
Wilhelm, B. et al. 1400 years of extreme precipitation patterns over the Mediterranean French Alps and possible forcing mechanisms. Quat. Res. 78, 1–12 (2012).
Wirth, S. B., Glur, L., Gilli, A. & Anselmetti, F. S. Holocene flood frequency across the Central Alps—solar forcing and evidence for variations in North Atlantic atmospheric circulation. Quat. Sci. Rev. 80, 112–128 (2013).
Czymzik, M. et al. Orbital and solar forcing of shifts in mid- to late Holocene flood intensity from varved sediments of pre-alpine Lake Ammersee (southern Germany). Quat. Sci. Rev. 61, 96–110 (2013).
Giguet-Covex, C. et al. Frequency and intensity of high-altitude floods over the last 3.5 ka in NW European Alps. Quat. Res. 77, 12–22 (2012).
Glur, L. et al. Frequent floods in the European Alps coincide with cooler periods of the past 2500 years. Sci. Rep. 3, 2770 (2013).
Wilhelm, B. et al. Palaeoflood activity and climatic changes over the last 1400 years from lake sediments of the NW European Alps. J. Quat. Sci. 28, 189–199 (2013).
Wilhelm, B. et al. Does global warming favour the occurrence of extreme floods in European Alps? First evidences from a NW Alps proglacial lake sediment record. Clim. Change 113, 563–581 (2012).
Evin, G., Wilhelm, B. & Jenny, J. P. Flood hazard assessment of the Rhône River revisited with reconstructed discharges from lake sediments. Glob. Planet. Change 172, 114–123 (2019).
Wirth, S. B. et al. Combining sedimentological, trace metal (Mn, Mo) and molecular evidence for reconstructing past water-column redox conditions: the example of meromictic Lake Cadagno (Swiss Alps). Geochim. Cosmochim. Acta 120, 220–238 (2013).
Irmler, R., Daut, G. & Mäusbacher, R. A debris flow calendar derived from sediments of Lake Lago di Braies (N. Italy). Geomorphology 77, 69–78 (2006).
Wilhelm, B., Vogel, H., Crouzet, C., Etienne, D. & Anselmetti, F. S. Frequency and intensity of palaeofloods at the interface of Atlantic and Mediterranean climate domains. Climate 12, 299–316 (2016).
Wilhelm, B., Vogel, H. & Anselmetti, F. S. A multi-centennial record of past floods and earthquakes in Valle d’Aosta, Mediterranean Italian Alps. Nat. Hazards Earth Syst. Sci. 17, 613–625 (2017).
Wirth, S. B. et al. A 2000-year long seasonal record of floods in the southern European Alps. Geophys. Res. Lett. 40, 4025–4029 (2013).
Swierczynski, T. et al. Mid- to late Holocene flood frequency changes in the northeastern Alps as recorded in varved sediments of Lake Mondsee (Upper Austria). Quarternary Sci. Rev. 80, 78–90 (2013).
Amann, B., Szidat, S. & Grosjean, M. A millennial-long record of warm season precipitation and flood frequency for the North-western Alps inferred from varved lake sediments: implications for the future. Quat. Sci. Rev. 115, 89–100 (2015).
Sabatier, P. et al. 6-kyr record of flood frequency and intensity in the western Mediterranean Alps—interplay of solar and temperature forcing. Quat. Sci. Rev. 170, 121–135 (2017).
Wirth, S. B., Girardclos, S., Rellstab, C. & Anselmetti, F. S. The sedimentary response to a pioneer geo‐engineering project: tracking the Kander River deviation in the sediments of Lake Thun (Switzerland). Sedimentology 58, 1737–1761 (2011).
Lauterbach, S. et al. DecLakes participants. A sedimentary record of Holocene surface runoff events and earthquake activity from Lake Iseo (Southern Alps, Italy). Holocene 22, 749–760 (2012).
Rapuc, W. et al. Holocene-long record of flood frequency in Southern Alps (Lake Iseo, Italy) under human and climate forcing. Glob. Planet. Change 175, 160–172 (2019).
Stewart, M., Grosjean, M., Kuglitsch, F. G., Nussbaumer, S. U. & von Gunten, L. Reconstructions of late Holocene palaeofloods and glacier length changes in the Upper Engadine, Switzerland (ca. 1450 BC–AD 420). Palaeogeogr. Palaeoclimatol. Palaeoecol. 311, 215–123 (2011).
Bajard, M. et al. Pastoralism increased vulnerability of a subalpine catchment to flood hazard through changing soil properties. Palaeogeogr. Palaeoclimatol. Palaeoecol. 538, 109462 (2019).
Fouinat, L. et al. Relationship between glacial activity and flood frequency in proglacial Lake Muzelle. Quat. Res. 87, 407–422 (2017).
Wilhelm, B. et al. Interpreting historical, botanical, and geological evidence to aid preparations for future floods. WIREs Water 6, e1318 (2018).
Parajka, J. et al. Seasonal characteristics of flood regimes across the Alpine–Carpathian range. J. Hydrol. 394, 78–89 (2010).
Blöschl et al. Current European flood-rich period exceptional compared with past 500 years. Nature 583, 560–566 (2020).
Schurer, A. P. et al. Small influence of solar variability on climate over the past millennium. Nat. Geosci. 7, 104–108 (2014).
Jones, P. D., Osborn, T. J. & Briffa, K. R. The evolution of climate over the last millennium. Science 292, 662–666 (2001).
Renssen, H. et al. The spatial and temporal complexity of the Holocene thermal maximum. Nat. Geosci. 2, 411–414 (2009).
Mudelsee, M. et al. No upward trends in the occurrence of extreme floods in central Europe. Nature 425, 166–169 (2003).
Beniston, M. & Stoffel, M. Rain-on-snow events, floods and climate change in the Alps: events may increase with warming up to 4 °C and decrease thereafter. Sci. Total Environ. 571, 228–236 (2016).
Moran-Tejeda, E., Lopez-Moreno, J. I., Stoffel, M. & Beniston, M. Rain-on-snow events in Switzerland: recent observations and projections for the 21st century. Clim. Res. 71, 111–125 (2016).
Magny, M., Bégeot, C., Guiot, J. & Peyron, O. Contrasting patterns of hydrological changes in Europe in response to Holocene climate cooling phases. Quat. Sci. Rev. 22, 1589–1596 (2003).
Magny, M. et al. North–south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses. Climate 9, 2043–2071 (2013).
Goosse, H., Guiot, J., Mann, M. E., Dubinkina, S. & Sallaz-Damaz, Y. The medieval climate anomaly in Europe: comparison of the summer and annual mean signals in two reconstructions and in simulations with data assimilation. Glob. Planet. Change 84-85, 35–47 (2012).
Yin, J. H. A consistent poleward shift of the storm tracks in simulations of 21st century climate. Geophys. Res. Lett. 32, L18701 (2005).
Shi, X. & Durran, D. The response of orographic precipitation over idealized midlatitude mountains due to global increases in CO2. J. Climatol. 27, 3938–3956 (2014).
Bengtsson, L. & Hodges, K. I. Storm tracks and climate change. J. Clim. 19, 3518–3543 (2006).
Raible, C. C., Yoshimori, M., Stocker, T. F. & Casty, C. Extreme midlatitude cyclones and their implications for precipitation and wind speed extremes in simulations of the Maunder Minimum versus present day conditions. Clim. Dyn. 28, 409–423 (2007).
St. George, S., Hefner, A. M. & Avila, J. Paleofloods stage a comeback. Nat. Geosci. 13, 766–768 (2020).
Harrison, S. P. et al. Evaluation of CMIP5 palaeo-simulations to improve climate projections. Nat. Clim. Change 5, 735–743 (2015).
Jenny, J. P. et al. A 4D sedimentological approach to reconstructing the flood frequency and intensity of the Rhône River (Lake Bourget, NW European Alps). J. Paleolimnol. 51, 469–483 (2014).
Reimer, P. J. et al. IntCal13 and Marine13 radiocarbon age calibration curves 0–50,000 years cal BP. Radiocarbon 55, 1869–1887 (2013).
Blaauw, M. Methods and code for ‘classical’ age-modelling of radiocarbon sequences. Quat. Geochronol. 5, 512e518 (2010).
R Development Core Team R: a Language and Environment for Statistical Computing (R Foundation for Statistical Computing, 2011); http://www.R-project.org/
Arnaud, F. et al. Erosion under climate and human pressures: an alpine lake sediment perspective. Quat. Sci. Rev. 152, 1–18 (2016).
Affolter, S. et al. Central Europe temperature constrained by speleothem fluid inclusion water isotopes over the past 14,000 years. Sci. Adv. 5, eeav3809 (2019).
Masson-Delmotte, V. et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) Ch. 5 (Cambridge Univ. Press, 2013).
Holzhauser, H., Magny, M. & Zumbühl, H. J. Glacier and lake-level variations in west-central Europe over the last 3500 years. Holocene 15, 789–801 (2005).
Newcombe, R. G. Interval estimation for the difference between independent proportions: comparison of eleven methods. Stat. Med. 17, 873–890 (1998).
Hamed, K. H. & Ramachandra, R. A modified Mann–Kendall trend test for autocorrelated data. J. Hydrol. 204, 182–196 (1998).
The data collection and the study design have been facilitated by the PAGES Floods Working Group that fosters collaborations. Sediment coring on Lake Bourget was performed using the French national sediment coring facility C2FN, in the framework of the excellence equipment project Equipe CLIMCOR (11-EQPX-0009, W.R., F.A., P.S. and B.W.) funded by the French National Agency for Research, ANR. The study of Lake Bourget sediment cores was performed in the framework of the CRIT-LAKES project funded by the Université Savoie Mont Blanc and the national CNRS programme EC2CO BIOHEFECT. The data analysis was performed in R using the supporting package trend. The authors acknowledge comments on preliminary publication versions from J.D. Creutin, G. Durand, C. Obled and M. Ménégoz as well as further colleagues for informal discussion during our Friday’s beer.
The authors declare no competing interests.
Peer review information
Nature Geoscience thanks Samuel Munoz and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: James Super.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended Data Fig. 1 Data acquired to extend the 350-year paleoflood record of the Rhône River to the the last millennium.
Data acquired to extend the 350-year paleoflood record of the Rhône River to the the last millennium. The method used is identical to Jenny et al. (2014)56. (A) Bathymetry of Lake Bourget and coring sites from Jenny et al. (2014)56 and from the 2017 campaign (this study). (B) Stratigraphical correlation of the two core datasets along transect A and B, with indications of historical flood dates56 and radiocarbon samples (Extended Data Table 4). (C) Age-depth model based on historical flood events and radiocarbon ages, using the software-package ‘clam’58.
Evaluation of the newly reconstructed Lake Bourget palaeoflood record over the last 350 years (a) and the last two millennia (b). Over the last 350 years, the new record (b.) is compared to the record from Evin et al. (2019)23(a.), which is an update of the dataset from Jenny et al. (2014)56 that combined reconstructed palaeoflood discharges from 1650 to 1852 (black squares) and annual flood discharges from 2010 to 1852 (black and red dots). Red dots denote the floods recorded in the sedimentary sequence among the gauged, annual floods (black dots). Our new record includes 27 on these 32 floods and the five extreme floods correspond well to the largest flood discharges. The lacking floods in our dataset can be related to the lower number of sediment cores compared to Jenny et al. (2014)56 and Evin et al. (2019)23. Over the last 2000 years, the new record (d) is compared to the record from Arnaud et al. (2016)60, which correspond to detrital inputs brought by the Rhône River floods to the deepest part of Lake Bourget. These detrital inputs were very low in the oldest part of the record and largely increased during the Little Ice Age. This period of increased detrital inputs corresponds well to higher occurrence of flood events. Therefore, these comparisons support the robustness of our extended Rhône River palaeoflood record.
About this article
Cite this article
Wilhelm, B., Rapuc, W., Amann, B. et al. Impact of warmer climate periods on flood hazard in the European Alps. Nat. Geosci. 15, 118–123 (2022). https://doi.org/10.1038/s41561-021-00878-y